1. Field of Use
This invention generally relates to impact resistant explosion proof lamps comprising enclosed or encapsulated light sources. In particular, it relates to such lamps wherein one or more light sources are encapsulated as by casting in several layers of transparent materials which have different elasticities.
2. Description of the Prior Art
Electric lamps are known in which a light source is placed into a transparent casing and tightly enclosed therein (see German Patent DGM No. 1,833,690). In other versions, one or several light sources are directly and tightly surrounded with transparent cast polyester or similar material and designated as "explosion-proof" (see British Pat. No. 1,166,442 and U.S. Pat. No. 3,310,670).
The latest technology further includes electric lighting devices for the marking of airplane landing strips with a trough-type housing submerged in the runway surface, which is covered by a transparent plate or a slotted cover plate, and in which housings light sources are mounted which can be switched on and off from the outside (see CH-PS 355 360).